The invention is directed to a method for in situ identification of the sheet resistivity or, respectively, of process parameters of thin, electrically conductive layers manufactured under the influence of a plasma, as utilized, in particular, in semiconductor and thin-film technology, on the basis of a two-point or four-point measuring method. The invention is also directed to applications of the measuring method.
European Patent 0 146 720 corresponding to U.S. Pat. No. 4,562,089 discloses a method of the said species.
Thin-electrically conductive layers are indispensable for, for example, layers of mechanically resistant material, optical coating layers on glasses and, in particular, in microelectronics for the wiring of integrated semiconductor components on a silicon substrate. The stricter and stricter demands made of such layers require a reproducible, utmost layer quality in their manufacture and, thus, require an intense process monitoring that should best ensue in situ, i.e., during the manufacture, in order to obtain maximum information about the process. Moreover, multi-chamber systems, wherein a plurality of process steps with deposition or structuring successively ensue in a plurality of process chambers without interrupting the vacuum, are being increasingly employed in semiconductor and thin-film technology. Since the layer properties change when leaving the vacuum or, respectively, during cooling, an in situ monitoring is desired even in multi-chamber systems since the condition of the layers in the vacuum system is not correctly reflected by subsequent measurements and the course of the status of the layer formation cannot be tracked and controlled in the process.
Typical parameters characterizing a conductive, layer, particularly metal, are structure and constitution as well as stoichiometry. A good measure for these parameters are the electrical properties of the layer, i.e., its resistance.
Although European Patent 0 067 432 corresponding to U.S. Pat. No. 4,543,576 discloses an arrangement for measuring the resistance and the temperature of metallic layers deposited by vapor deposition or sputtering onto substrates during the production of the layer, the method known therefrom is based on the employment of a reference substrate, similar to other known methods. Therefore, measurements can not be undertaken at arbitrary locations directly at the substrate to be processed; rather, specific contacting measures must be undertaken at a specific reference wafer which can then often no longer be integrated into the manufacturing process. In the known arrangement, whereby the measured data are telemetrically transmitted to a receiver, the measurement and transmission electronics is attached in the process chamber, this producing further disadvantages. For example, the temperature stability is low and the process chamber is unavoidably contaminated by exhaust gases of the electronic components, whereas, also, the measuring arrangement itself is not resistant to, for example, aggressive gases that occur given etching plasmas.
Plasma-enhanced etching and deposition processes are being more frequently utilized. An even greater problem in view of measuring a sheet resistivity during the manufacture of the layer or, respectively, of the structure, is inaccurate measurements due to the presence of the plasma. The electrical sheet resistivity measured in situ is falsified as soon as the forming layer comes into the influencing area of the plasma. In, for example, cathode sputtering, in vapor phase deposition (PECVD), or when structuring in RIE, MERLE or ECR reactors, disturbances are induced by the plasma that can often exceed the useful signal by more than 50% and thus cause a considerable mismeasurement. In view of current demands, however, even less than 10% mismeasurement is no longer acceptable in practice.
Among other things, the aforementioned European Patent 0 146 720 proposes a method for measuring the sheet resistivity despite the influence of the plasma, in that the electrical resistance or the voltage drop-off across the layer is identified by at least two, successive, different measuring currents I.sub.M1 and I.sub.M2 having a known size, whereby the measuring currents are selected corresponding to the sheet resistivity and the difference between the measuring currents employed is selected in the region of the relationship 2 through 100. Apart therefrom that the implementation of the known method is dependent on a telemetry system, it has turned out, as shall be set forth in greater detail below, that a complete elimination of the influence of the plasma is not possible in the known method, for fundamental electro-technical reasons.
In addition to the sheet resistivity described previously, a monitoring of the process parameters defining the sheet resistivity is also necessary. The layer parameters can be kept within desired, narrow tolerances by adjusting the process parameters. Up to now, monitoring or, respectively, control methods only existed for pressure, power, gas flow or residual gas quality, whereas quantities such as ion current, floating potential or internal plasma resistance that directly relate to the plasma were incapable of being identified with reasonable outlay. The measurement of the direct layer temperature was also previously difficult to design since a specific test substrate, for example having an applied resistance thermometer must be generally employed for that purpose. Added thereto is again the sensitivity to a plasma influence deriving from the variable resistance.